1. Field of the Invention
One embodiment of the invention relates to a communication system, a transmitter and a receiver which provide interactive communications via a communication path.
2. Description of the Related Art
In recent years, as an IC chip to be mounted on an IC card attains high performance, an IC card (portable electronic device) capable of executing a plurality of applications has been made practicable. Such an IC card executes various kinds of processing by obtaining a power supply from a dedicated reader/writer (electronic processing terminal).
When the IC card and reader/writer communicates with each other, a communication path is established. The portable electronic device is connected to one end of the communication path, and the electronic processing terminal is connected to the other end thereof. A technique, which transmits and receives binary data between the portable electronic device and the electronic processing terminal by switching a state (a high level) in which a large current is applied to the communication path and a state (a low level) in which no current is applied thereto in the connection state mentioned above, is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-68720.
In the technique of the above, data is transmitted and received, for example, by replacing the data expressed in hexadecimal notation with a binary system. When the data is transmitted and received, a start bit and a stop bit is added to a data section which has been replaced with the binary system.
A transmission circuit of the transmitter applies a voltage to the communication path in response to the data expressed by the binary system. When transmitting a bit expressed by “1” in the binary system, the transmission circuit applies a voltage of the high level to the communication path. When transmitting a bit expressed by “0” in the binary system, the transmission circuit applies a voltage of the low level to the communication path. Thereby, the transmission circuit of the transmitter switches a state in which any current is applied to the communication path and a state in which any current is not applied thereto.
A reception circuit of the receiver measures a state flowing in the communication path to analyze the measurement result and then receives the data.
However, in the technique of the above, transmitting data with many bits which make current flows such as “FF” in hexadecimal notation, namely, “11111111” in the binary system poses a problem that large power is consumed.